Bug in GenericApproachDescriptor (was ACTS-254)

Original author Julia Hrdinka @jhrdinka

On the edge of a layer, there is a region, where the outer approaching surface of a layer is not hit anymore, when extrapolating in a straight line, starting from the origin, but the inner approaching surface of this layer should still be hit. It was found that this was not the case and that the inner approaching surface was cut on the edges, when the outer approaching surface was not hit anymore. The bug was found in the GenericApproachDescriptor in the function approachSurface, which returns the closest approaching surface.